1. Field of the Invention
The present invention relates to a display device, and more particularly to a stereoscopic video display device having a lens array unit.
2. Description of the Related Art
There are known various types of stereoscopic image display devices, so-called tree dimension displays, which can display motion video. In recent years, in particular, in the field of flat-panel type displays, there has been an increasing demand for a method that requires no special eyeglasses. Of this type of stereoscopic motion video display devices, a display device that uses the principle of holography can hardly realize full-color motion video. However, full-color motion video can relatively easily be realized by a method in which a light ray control element, which controls light rays from a display unit and turns the light rays to the viewer, is disposed immediately before the display unit (display device) with fixed pixel positions, such as a direct-viewing type or projection type liquid crystal display device or plasma display device.
The light ray control element is generally called “parallax barrier”. The light ray control element controls light rays so that different images can be viewed depending on angles, even at the same position on the light ray control element. Specifically, when only right-and-left parallax (horizontal parallax) is imparted, a slit or a lenticular lens sheet (cylindrical lens array) is used. In the case where up-and-down parallax (vertical parallax) is also imparted, a pinhole array or a lens array comprising matrix-arrayed lenses is used. The methods using parallax barriers are further classified into a two-view (binocular) type, a multi-view type, a super-multi-view type (super-multi-view condition of a multi-view type), and integral photography (hereinafter also referred to as “IP”). The basic principle of these methods is substantially the same as the principle that was invented about 100 years ago, and has been used in the field of stereoscopic photography.
Of these methods, the IP method is characterized by a high degree of freedom of view-point position and easy realization of stereoscopic view. In a one-dimensional IP method in which only horizontal parallax is provided and vertical parallax is not provided, a display device with high resolution is relatively easily realized (see, e.g. SID04 Digest 1438 (2004)). On the other hand, as regards the two-view type and multi-view type, there is a problem that the range of viewing-point position which permits stereoscopic view, that is, the visual range, is narrow and there is difficulty in viewing. However, these types are simplest in structure as stereoscopic image display devices, and a display image can easily be created.
It is desirable that the light ray control element be precisely fixed to the display unit with a proper gap being kept from the display unit. Various methods have been developed for fixing a lens array unit, which is one of light ray control elements, to the display unit. Jpn. Pat. Appln. KOKAI Publication No. 11-202313, for instance, discloses a liquid crystal display device wherein a second substrate, on which a micro-lens is disposed, is used on a cover-glass-side outer surface in order to effectively increase the aperture ratio of the pixel, although this liquid crystal display device is not related to the stereoscopic image display apparatus. In particular, this document discloses the structure in which a spacer having the same height as the micro-lens is provided at the outer periphery of the micro-lens on the glass substrate on which the micro-lens is formed, and the glass substrate is attached to the outer surface of the cover glass via the spacer.
In addition, Jpn. Pat. Appln. KOKAI Publication No. 2006-039265, for instance, discloses a micro-lens array plate which has a reduced-pressure layer between a first transparent substrate, on which a lens surface of a micro-lens is formed, and a second transparent substrate that is opposed to the first transparent substrate, with a view to attaining structural stability, and an electrooptical device (liquid crystal device) including this micro-lens array plate, although this technique does not relate to the stereoscopic image display device.
In order to obtain sufficient stereoscopic display characteristics, various design parameters need to be optimized. In particular, in order to obtain desired display characteristics, it is very important to make uniform the lens-pixel gap in the display area in the structure in which the lens array unit and the display unit are combined.